mber having an aneurism； while others cut down upon the tumor itself and attempted to tie off the artery above and below。 The first of these operations maimed the patient for life； while the second was likely to prove fatal。
In pondering over what he had learned about collateral circulation and the time required for it to become fully established； Hunter conceived the idea that if the blood…supply was cut off from above the aneurism； thus temporarily preventing the ceaseless pulsations from the heart； this blood would coagulate and form a clot before the collateral circulation could become established or could affect it。 The patient upon whom he performed his now celebrated operation was afflicted with a popliteal aneurismthat is； the aneurism was located on the large popliteal artery just behind the knee…joint。 Hunter； therefore； tied off the femoral； or main supplying artery in the thigh； a little distance above the aneurism。 The operation was entirely successful； and in six weeks' time the patient was able to leave the hospital； and with two sound limbs。 Naturally the simplicity and success of this operation aroused the attention of Europe； and； alone； would have made the name of Hunter immortal in the annals of surgery。 The operation has ever since been called the 〃Hunterian〃 operation for aneurism； but there is reason to believe that Dominique Anel （born about 1679） performed a somewhat similar operation several years earlier。 It is probable； however； that Hunter had never heard of this work of Anel； and that his operation was the outcome of his own independent reasoning from the facts he had learned about collateral circulation。 Furthermore； Hunter's mode of operation was a much better one than Anel's； and； while Anel's must claim priority； the credit of making it widely known will always be Hunter's。
The great services of Hunter were recognized both at home and abroad； and honors and positions of honor and responsibility were given him。 In 1776 he was appointed surgeon…extraordinary to the king； in 1783 he was elected a member of the Royal Society of Medicine and of the Royal Academy of Surgery at Paris； in 1786 he became deputy surgeon…general of the army； and in 1790 he was appointed surgeon…general and inspector…general of hospitals。 All these positions he filled with credit； and he was actively engaged in his tireless pursuit of knowledge and in discharging his many duties when in October； 1793； he was stricken while addressing some colleagues； and fell dead in the arms of a fellow…physician。
LAZZARO SPALLANZANI
Hunter's great rival among contemporary physiologists was the Italian Lazzaro Spallanzani （1729…1799）； one of the most picturesque figures in the history of science。 He was not educated either as a scientist or physician； devoting； himself at first to philosophy and the languages； afterwards studying law； and later taking orders。 But he was a keen observer of nature and of a questioning and investigating mind； so that he is remembered now chiefly for his discoveries and investigations in the biological sciences。 One important demonstration was his controversion of the theory of abiogenesis； or 〃spontaneous generation；〃 as propounded by Needham and Buffon。 At the time of Needham's experiments it had long been observed that when animal or vegetable matter had lain in water for a little timelong enough for it to begin to undergo decompositionthe water became filled with microscopic creatures； the 〃infusoria animalculis。〃 This would tend to show； either that the water or the animal or vegetable substance contained the 〃germs〃 of these minute organisms； or else that they were generated spontaneously。 It was known that boiling killed these animalcules； and Needham agreed； therefore； that if he first heated the meat or vegetables； and also the water containing them； and then placed them in hermetically scaled jarsif he did this； and still the animalcules made their appearance； it would be proof…positive that they had been generated spontaneously。 Accordingly be made numerous experiments； always with the same resultsthat after a few days the water was found to swarm with the microscopic creatures。 The thing seemed proven beyond questionproviding； of course； that there had been no slips in the experiments。
But Abbe Spallanzani thought that he detected such slips in Needham's experiment。 The possibility of such slips might come in several ways： the contents of the jar might not have been boiled for a sufficient length of time to kill all the germs； or the air might not have been excluded completely by the sealing process。 To cover both these contingencies； Spallanzani first hermetically sealed the glass vessels and then boiled them for three…quarters of an hour。 Under these circumstances no animalcules ever made their appearancea conclusive demonstration that rendered Needham's grounds for his theory at once untenable。＇2＇
Allied to these studies of spontaneous generation were Spallanzani's experiments and observations on the physiological processes of generation among higher animals。 He experimented with frogs； tortoises； and dogs； and settled beyond question the function of the ovum and spermatozoon。 Unfortunately he misinterpreted the part played by the spermatozoa in believing that their surrounding fluid was equally active in the fertilizing process； and it was not until some forty years later （1824） that Dumas corrected this error。
THE CHEMICAL THEORY OF DIGESTION
Among the most interesting researches of Spallanzani were his experiments to prove that digestion； as carried on in the stomach； is a chemical process。 In this he demonstrated； as Rene Reaumur had attempted to demonstrate； that digestion could be carried on outside the walls of the stomach as an ordinary chemical reaction； using the gastric juice as the reagent for performing the experiment。 The question as to whether the stomach acted as a grinding or triturating organ； rather than as a receptacle for chemical action； had been settled by Reaumur and was no longer a question of general dispute。 Reaumur had demonstrated conclusively that digestion would take place in the stomach in the same manner and the same time if the substance to be digested was protected from the peristalic movements of the stomach and subjected to the action of the gastric juice only。 He did this by introducing the substances to be digested into the stomach in tubes； and thus protected so that while the juices of the stomach could act upon them freely they would not be affected by any movements of the organ。
Following up these experiments； he attempted to show that digestion could take place outside the body as well as in it； as it certainly should if it were a purely chemical process。 He collected quantities of gastric juice； and placing it in suitable vessels containing crushed grain or flesh； kept the mixture at about the temperature of the body for several hours。 After repeated experiments of this kind； apparently conducted with great care； Reaumur reached the conclusion that 〃the gastric juice has no more effect out of the living body in dissolving or digesting the food than water； mucilage； milk； or any other bland fluid。〃＇3＇ Just why all of these experiments failed to demonstrate a fact so simple does not appear； but to Spallanzani； at least； they were by no means conclusive； and he proceeded to elaborate upon the experiments of Reaumur。 He made his experiments in scaled tubes exposed to a certain degree of heat； and showed conclusively that the chemical process does go on； even when the food and gastric juice are removed from their natural environment in the stomach。 In this he was opposed by many physiologists； among them John Hunter； but the truth of his demonstrations could not be shaken； and in later years we find Hunter himself completing Spallanzani's experiments by his studies of the post…mortem action of the gastric juice upon the stomach walls。
That Spallanzani's and Hunter's theories of the action of the gastric juice were not at once universally accepted is shown by an essay written by a learned physician in 1834。 In speaking of some of Spallanzani's demonstrations； he writes： 〃In some of the experiments； in order to give the flesh or grains steeped in the gastric juice the same temperature with the body； the phials were introduced under the armpits。 But this is not a fair mode of ascertaining the effects of the gastric juice out of the body； for the influence which life may be supposed to have on the solution of the food would be secured in this case。 The affinities connected with life would extend to substances in contact with any part of the system： substances placed under the armpits are not placed at least in the same circumstances with those unconnected with a living animal。〃 But just how this writer reaches the conclusion that 〃the experiments of Reaumur and Spallanzani give no evidence that the gastric juice has any peculiar influence more than water or any other bland fluid in digesting the food〃＇4＇ is difficult to understand。
The concluding touches were given to the new theory of digestion by John Hunter； who； as we have seen； at first opposed Spallanzani； but who finally became an ardent champion of the chemical theory。 Hunter now carried Spallanzani's experiments further and proved the action of the digestive fluids after death。 For many years anatomists had been puzzled by pathological lesion of the stomach； found post mortem； when no symptoms of any disorder of the stomach had been evinced during life。 Hunter rightly conceived that these lesions were caused by the action of the gastric juice； which； while unable to act upon the living tissue； continued its action chemically after death； thus digesting the walls of the stomach in which it had been formed。 And； as usual with his observations； be turned this discovery to practical use in accounting for certain phenomena of digestion。 The following account of the stomach being digested after death was written by Hunter at the desire of Sir John Pringle； when he was president of the Royal Society； and the circumstance which led to this is as follows： 〃I was opening； in his presence； the body of a patient of his own； where the stomach was in part dissolved； which appeared